1. Field of the Invention
The present invention relates to the field of medical radiography; and more particularly to means for positively identifying the exposure side or front side of an X ray film.
2. Description of the Prior Art
A medical radiograph is the X ray image of some part of the body produced by an X ray beam originating from an X ray tube. The X ray beam passes first through the body and then through an X ray film cassette which is a light-proof, flat box of rigid construction. It is typically comprised of a base with a central recess to receive the film, and a cover joined to the base by hinges and containing latches permitting it to be opened and securely closed when a film is loaded. In order to diminish the X ray dose required to obtain a proper exposure of the film the inside surfaces of the cassette are lined with "intensifying screens" which sandwich the film between them. The X ray beam passing through the intensifying screens causes them to fluoresce and give off visible light which in turn exposes the film from both sides. Since the X ray film is much more sensitive to the visible light than to the X ray beam, most of the film exposure actually results from the induced light. The presence of the screens therefore allows the optimal film exposure to be achieved at significantly lower radiation doses than would otherwise be needed. Once the film is exposed, it is brought to the dark room, removed from the cassette and developed, causing the latent image to become visible. The radiograph is then ready for viewing and interpretation.
Since the film must be identified with pertinent information such as patient's name, date, etc., the cassette is also provided with what is herein called a "blocker". This blocker is generally comprised of two opposing strips of lead mounted on the inside surfaces of the cassette which shield the area of film between them from becoming exposed by either the X ray beam or its induced light. When the technologist is ready to develop the film, a card bearing the appropriate patient data is placed into a device which light-flashes the card, thereby projecting the data onto the unexposed area shielded by the blocker. The position of the blocking rectangle within the cassette is not constant and may vary with the manufacturer, individual X ray department, and even from one cassette type to another within the same department.
Apparatus and methods, including modifications of the film cassette for marking exposed X ray film or radiographs with patient data are disclosed, for example by U.S. Pat. Nos. 3,628,864, 3,703,272, 4,465,364, 4,510,392, 4,806,959, 4,383,329, 4,520,497, and 4,768,114.
When rendering a diagnosis from a radiograph it is necessary for the film reader to know which side of the body is being viewed. Since the body is generally symmetrical, right-sided structures are similar in appearance to left-sided structures except that they are mirror-images or reversals of one another. For example, an X ray image of a left foot if viewed from the back /f the exposed film will look like a right foot. Since radiographs are typically transparent and can be viewed from either side, it is therefore possible for X ray images of one side of the body to become confused with the other. For this reason when a medical radiograph is performed of some part of the body it is customary for the technologist to affix and X ray opaque "R" or "L" marker on the cassette cover adjacent to the part being X-rayed to indicate which side of the body is represented on the film. Not infrequently however, the technologist places the wrong marker on the cassette or for one reason or another the marker is not visible on the film, being either obscured or omitted, so that the technologist is required to mark the film after it is developed, using an adhesive label, wax pencil, ink, or even scratch marks. The incidence of incorrect or absent right/left marking due to human error is quite substantial, reportedly as high as 30%. If a film is improperly marked and the physician interpreting the film recognizes the error he will often try to locate the technologist who performed the study to obtain clarification. When the question cannot be resolved in this manner, the patient may be recalled for a repeat examination which involves time, inconvenience, expense and additional radiation exposure. Furthermore, if the error should go undetected, inappropriate medical treatment may be the result.
Since the primary cause of this right/left confusion stems from the fact that the film is transparent and may be viewed from the front (exposure side) or the back, identifying the front side of the film for the viewer will prevent the inadvertent viewing of the film from the wrong side and thereby permit ready determination of which side of the body is represented thereon.
There is no means described in the prior art for permanently modifying the film cassette to expressly indicate the exposure side of the film, positively and regardless of the direction of exposure.